This disclosure generally relates to systems and methods for responding to transient conditions in power generation systems and more particularly to a power conversion system, a method for controlling the power conversion system and a wind turbine power generation system.
Wind turbines are becoming increasingly used as a source of renewable energy by utility companies. One approach to achieving efficient conversion of mechanical power from blades of a wind turbine into electrical energy supplied to a grid is the use of a doubly fed induction generator (DFIG) combined with a power electronics converter.
The DFIG includes a stator connected to the grid and a rotor connected between the wind turbine and the grid. In some embodiments, a gearbox is used between the wind turbine and the DFIG to adjust a rotational speed. The power electronics converter is used to convert the mechanical power into electronic power which is then provided to the grid. In one embodiment, the power electronics converter includes a source side converter, a line side converter, a DC link connecting the two converters, and one or more controllers for the source side and line side converters.
Wind turbines often operate in complicated conditions which impose high mechanical stresses. At the wind turbine side, during grid fault or wind gust conditions, the mismatch of electrical torque and mechanical torque may result in huge mechanical stress on a tower of the wind turbine and the gearbox, which may cause the tower to shift and potentially sustain damage. Additionally, electrical torque oscillations may influence the mechanical system's lifetime and cost. At the grid side, when electrical power is converted and provided to the grid, if an impedance mismatch is present, some sub-sync oscillations (SSO) or low frequency oscillations (LFO) may occur within the voltage and current provided to the grid. Such oscillations may cause undesired harmonic distortion.
Therefore, it is desirable to provide improved systems and methods to address at least one of the above-mentioned problems.